Denise Lewis will join other leading figures, including Sir Richard Branson, on a world tour to promote Britain in Olympic year. Photograph: John Gichigi/Getty Images

The government has insisted its increasing determination to invest in making the 2012 Olympics a large-scale advert for Britain has not diminished its desire to honour the legacy promises that secured them.

Announcing a £39m promotional campaign designed to capitalise on London 2012, the culture secretary, Jeremy Hunt, said the so-called "Great" marketing push and the decision to double the ceremonies budget to £81m would guarantee the Games showcased the country's strengths in business, tourism and education.

Hunt promised the opening ceremony would be "mind-blowing" but said that there was no move to distance the government from the wide-ranging legacy promises that secured the Games in favour of a month-long advert for the nation. "This is not spending money on a party. This is investing in Britain's future," he said. "Future generations would never forgive us if we didn't grasp the opportunity of hosting the Olympics to create jobs for British businesses."

The government has faced criticism for cutting the ringfenced national budget for school sport by half and abandoning an inherited target to increase the number of people playing regular sport by one million by 2013. Hunt is expected to announce new policies designed to address those issues next week. "We remain 150% true to the vision Seb [Coe] outlined in Singapore in 2005. We remain totally committed to that," he said. "It's a difficult period in terms of public spending. I think we've got a very good plan in place that will convince the sceptics we can deliver on a fantastic sporting legacy as well as a fantastic economic legacy."

Hunt has replaced all the art in his office with 2012 prints – Tracey Emin's being his favourite. But he will see little of it in the coming months, as he joins leading British figures – including Sir Richard Branson, Vivienne Westwood, Paul Smith and Denise Lewis – on a world tour of 17 cities in Brazil, China, the US, France, Germany, Japan, Australia, India and Canada to "bang the drum" and promote British interests.

"This is the government completely ignoring all the siren voices that say in times of austerity we should be cutting back on promotion," Hunt said. "We're not staying in the middle ground, we're doing the opposite of what those siren voices are saying. This is a once-in-a-generation opportunity to promote the UK. Sport has a reach nothing else can match. We know around half the world's population will watch the Olympics live at some stage. That's something nothing else can compete with."

The campaign will target cities selected to give "most bang for our buck" with a marketing blitz, including a projection on Sugarloaf Mountain in Rio de Janeiro, magazine adverts designed to reach two million Parisians and a tie-up with India Today at an economic summit in Delhi. Hunt claimed a campaign at 13 airports will reach 47 million travellers.

"We have to be prepared that there might be some sniping and unpopularity in investing in banging the drum for Britain when times are tough but what people want is a government that will get the country back on its feet," Hunt said. "If you don't grasp an opportunity like this I really think you'll be betraying a generation.

"My right arm is going to be so sore from waving the flag it's going to fall off by 9 September [the Paralympics closing ceremony]. People know Britain is an extraordinary country but we do sometimes have an innate modesty. If there's one time you should cast that aside it's when you're hosting the Olympics."

The government is targeting an additional £1bn of investment and trade, an additional £2.5bn in tourist spend and 4.5 million more visitors over the next four years. That will be a huge challenge, given that previous Games have tended to depress tourism numbers.

Hunt also defended the decision to hand Locog an extra £41m from the public funding package to double the budget of the opening and closing ceremonies. "We went through a very detailed process," he said. "Danny Boyle is one of our most talented creative geniuses. He came up with these proposals and we went through them in enormous detail. We couldn't do everything Danny wanted but we wanted to stay true to his creative vision, which is extraordinary.

"We were very impressed with what we saw and in the end we were never in any doubt we wanted a totally mind-blowing opening ceremony."

Hunt said he remained confident that the £9.3bn budget would be sufficient, despite the National Audit Office having warned that there was a "real risk" it would be breached, but admitted there was little margin for error.

"I'm as confident as I can be. You never know what is around the corner, but we have managed the budget in a very rigorous way. All the risks going forward are quantified. If you look at the figures in a reasonable way, you'd say we should be all right. There isn't a huge amount of room for manoeuvre but if we continue to bear down on costs we should be able to deliver."

He said Olympic sceptics would be forced to re-examine their attitudes by the time of the opening ceremony on 27 July. "I'm continually surprised by how few naysayers there are. I was expecting there to be a much higher volume. If you look at the runup to Sydney and Vancouver, there were many, many more sceptics than there have been in the UK.

"Locog has done a superb job in helping get the public fully behind the Games. There will always be a few sceptics but the closer we get the more they are starting to realise that this is going to be an extraordinary moment and they will feel perhaps just a tinge of being a party pooper."